This standard expands students’ previous knowledge and mastery of addition to include up to four two-digit numbers at a time. Students understand that it is possible to add more than two mumbers. They are learning that even when there are more than two addends, they can extend the standard place-value algorithm for addition by adding all the ones together, and all of the tens together. They are also learning that they can sometimes make strategic choices of the order or grouping in which we add the numbers. For example, consider the addition problem 78 + 34 + 41 + 12. Students can start by adding 78 and 34 (and it is fine if students do this, providing they do it correctly). However, it is easier to group the 78 and 12 together, since they add up to a mulitple of 10. Reordering and regrouping the addends, we see that the sum (78 + 12) + (34 + 41) = 90 + 75 = 165.
Understanding the Standards:
- Addition with multiple addends should begin slowly, with the teacher making sure that there are no errors when students add just two addends together.
- Students can check their answers by adding the digits in the tens place and adding digits in the ones place, and finally, adding the two sums together.
- Students should have practice in rewriting a sum that is given horizontally so that it is in a vertical alignment. Careful attention should be given to proper alignment of digits. Teachers can check students' understanding of place value by also including numbers with just one digit.
- Teachers can encourage students to look for strategic ways to regroup and reorder addends, or use strategies such as compensation (increase one addend by a certain number, and decrease another addend by the same number).
Questions to Focus Instruction:
- Are students able to properly line up multiple addends in an addition problem when writing the addition problem in a vertical format?
- Can students add multiple addends by totaling the ones and totaling the tens (in any order) and then adding the totals together, regrouping if necessary?
- Can students use properties of operations to add up to four two-digit numbers in an efficient, fast, and accurate way?
Prior to: Students can add multiple addends fluently to a sum less than or equal to 20.
At Grade Level: Students can add multiple two-digit numbers using strategically chosen approaches.
Moving Beyond: Students will have experience with adding together much larger numbers through the 1000s. Their knowledge of place value, regrouping and addition strategies will be useful. See 2.NBT.7, 3.NBT.2, and 4.NBT.4.